Solid state imagers, including charge coupled devices (CCD) and CMOS sensors, are commonly used in photo-imaging applications. A solid state imager includes a focal plane array of pixels. Each of the pixels includes a photosensor device for converting light energy to electrical signals. The photosensor device can be a photogate, photoconductor, a photodiode or other solid state device having a doped region for accumulating photo-generated charge.
Color filter arrays are commonly placed over imager pixel arrays and may also be used in display devices over light emitting elements. In an imager, the color filter arrays are used to filter light of specific wavelengths into the initial charge accumulation region, for example. Color filter arrays are commonly arranged in a mosaic sequential pattern of red, green, and blue filters known as a Bayer filter pattern. The Bayer filter pattern is a quartet ordered with successive rows that alternate (a) red and green, then (b) green and blue filters. Thus, each red filter is surrounded by four green and four blue filters, while each blue filter is surrounded by four red and four green filters. In contrast, each green filter is surrounded by two red, four green, and two blue filters. The heavy emphasis placed upon green filters is due to human visual response, which reaches a maximum sensitivity in the 550-nanometer (green) wavelength region of the visible spectrum.
Conventional technology fabricates color filter arrays using evaporated colorants which do not involve any receiving polymer. To fabricate such color filter arrays over image sensors, the following typical process is used: A photoresist containing a colorant, generally a pigment, is deposited on a semiconductor substrate. The pigmented photoresist is patterned, leaving color pigment over the pixels. A photo develop puddle process is performed such that the pigment and photoresist is removed, but color pigment residue is left behind in the non-patterned areas, interfering with subsequent color filter array levels and degrading the overall image performance. FIG. 1 illustrates a Bayer pattern color filter array in plan view at one stage of processing according to the prior art. Red pigments 5 and blue pigments 6 have been deposited. In FIG. 1, green pigments have not yet been deposited; however, in accordance with the Bayer pattern, the green pigments are to be deposited in green regions 7. Blue pigments 6 remain in green regions 7 after the blue etch process, which is undesirable.
Differing photo develop puddle processes may be used to remove these residual pigments. However, puddle develop processes can cause serious degradation of the desired photo-developed pattern. In addition, puddle develop processes are affected by the topology of the existing substrate, the pattern of the color filter array, and spin effects from other steps of the color filter array processing.
Therefore, a process for cleaning the residual pigments from the color filter array resist levels without damaging the color filter array and that is independent of topology, pattern, and spin effects is desirable.